Peugeot's are known for airbag warning light (same engine etc as Citroen) there may be a connector under one of the passenger seats that is a bit loose - re-make it and it may just cure it.
That's it Gold. It was more of an issue in the early days and was usually the drivers seat where the problem was as that was the seat that was repositioned for different driver's heights.
But its always worth a try.
Before touching it though, window the window down, switch on the ignition and then remove the battery terminal making sure it is impossible to reconnect. Leave the van for 5 minutes, letting all the residual current in the system dissipate.
Once you have sorted the connections then switch the ignition off and then replace the battery terminal and see if the light goes out.
I'm surprised it wasn't an MOT failure.